The present invention relates to superhard articles of manufacture for use in many applications but preferably for use as mixing tubes for use in high-pressure abrasive water jet systems and methods for producing same. More particularly, the invention relates to mixing tubes using a superhard material, i.e. PCD (polycrystalline diamond) or electrically conductive PCBN (polycrystalline cubic boron nitride), in high pressure abrasive water jet systems and methods for producing same. The present invention also relates to abrasive water jet systems comprising an abrasive water jet mixing tube having a longitudinal bore lined with a superhard material.
High pressure abrasive water jet (AWJ) machining utilizes a very narrow stream of high pressure water laden with abrasive particles to erosion cut through a workpiece. AWJ machining is used in many industries, including the automobile, aerospace, computer, and glass industries, to create precision parts from a wide variety of materials such as plastics, metals, glass, composites, and ceramics, including those materials which are otherwise difficult to machine. The AWJ process machines with high precision, very little kerf, and produces a clean, smooth edge thereby reducing or eliminating the need for costly post-machining edge treatment operations. Because AWJ machining is a low temperature operation, it produces no heat affected zone in the machined part and can be used to machine heat treated parts without disturbing their heat treatment-induced material properties. AWJ machining heads may be guided by hand, machine, or computer with the most precise machining being obtained by computer-control of the AWJ machining head motion.
In a typical AWJ system, an intensifier pump is used to pressurize filtered water to the range of about 2,000 to 100,000 psi (14 to 690 MPa). The high pressure water is fed into an AWJ machining head where it is forced to pass through a nozzle orifice diameter as small as a few thousands of an inch (a few hundredths of a millimeter) to generate a high-velocity water jet. In commercial applications, abrasive particles such as garnet or olivine are introduced into the high-velocity water jet as it passes through a mixing chamber within the AWJ machining head. The abrasive particles and the high-velocity water jet mix as they travel together through the small diameter longitudinal bore of a mixing tube in the AWJ machining head to form upon exiting the mixing tube a narrow, abrasive, high-velocity water jet that is capable of making precise cuts through almost any kind of material.
An AWJ mixing tube longitudinal bore is subjected to severe jetting abrasion from the high-velocity water jet and abrasive particles it carries. However, the precision and the efficiency of AWJ machining is greatly affected by wear of the longitudinal bore of the mixing tube. Although the longitudinal bore diameters generally are on the order of 0.010 to 0.060 inches (0.25 to 1.5 mm) and the overall lengths of AWJ mixing tubes are usually on the order of 2 to 4 inches (5 to 10 cm), longitudinal bore diameter erosion of just a few thousands of an inch (a few hundredths of a millimeter) can greatly reduce the machining efficiency and degrade the machining precision, especially when the longitudinal bore erosion is near the exit end of the mixing tube. AWJ mixing tube longitudinal bore wear results in longer machining times, less precise machining, down time for replacing the worn mixing tube, and the cost of the replacement mixing tubes. To minimize this problem, AWJ mixing tubes are commonly made of a very hard materials, such as tungsten carbide.
In the past, there have been efforts to improve the wear resistance of AWJ mixing tubes by using chemically vapor-deposited (CVD) diamond as a longitudinal bore lining material. Diamond is an allotrope of carbon exhibiting a crystallographic network comprising covalently bonded, aliphatic sp3 hybridized carbon atoms arranged tetrahedrally with a uniform distance of 1.545 xc3x85 (0.1545 nm) between atoms and is extremely hard, having a Mohs hardness of 10. For example, Banholzer et al, U.S. Pat. No. 5,363,556, estimates that the use of diamond can extend the useful lifetime of AWJ mixing tubes from the about two to four hours obtained for conventional tungsten carbide mixing tubes to about twenty to one hundred hours.
Banholzer et al., supra, describes a method of making a AWJ mixing tube by depositing a diamond layer by CVD on a funnel shaped support member to form an inner member of diamond, separating the inner member from the support member, depositing an outer member material having a higher coefficient of thermal expansion than diamond on an outer side of the inner member to form an outer member of the mixing tube, and cooling the mixing tube to contract the outer member for inducing compressive stresses of sufficient strength on the inner member to substantially prevent the formation of cracks in the inner member. Anthony et al, U.S. Pat. No. 5,439,492, describes making a AWJ mixing tube by depositing a layer of diamond by CVD on a mandrel followed by removing the mandrel mechanically or by chemical etching to form the longitudinal bore of the mixing tube and then, optionally, providing a steel tube to support the diamond film. Stefanick et al., U.S. Pat. No. 5,785,582, describes depositing a layer of diamond by CVD on opposing sides of the longitudinal bore of a AWJ mixing tube made of a hard ceramic material that has been split longitudinally and then joining the two halves of the mixing tube together by shrink fitting a metal sheath around them.
There also have been efforts to use other forms of diamond and materials having hardnesses approximating that of diamond. Japanese Utility Model Application Laid-Open No. 63-50700, describes an AWJ mixing tube comprising a plurality of dies built in a sleeve main body. Each die consists of a knob of a polycrystalline sintered body of diamond or cubic crystal boron nitride, or the like, which is fixed to the inner circumference of an annular supporting stand metal of a tough material such as a super-hard alloy, high-speed steel, or the like. Each knob has a through-hole. However, the AWJ mixing tube described above has the disadvantage that wear occurs preferentially at the junction areas between the dies (see Examined Japanese Utility Model HEI-6-34936).
The inventors of the present invention have developed a method of producing an AWJ mixing tube with a longitudinal bore lined with a superhard material which does not require the use of diamond deposited by CVD. The present invention comprises methods for making an AWJ mixing tube using one or more pieces of a superhard material. The term xe2x80x9csuperhard materialxe2x80x9d as used herein refers to polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PCBN) which can be machined by electrical discharge machining (EDM). PCD is a particular species of synthetic diamond. PCD is produced by sintering together many individual diamond crystals in the presence of a catalyst at high temperatures and pressures into a coherent mass of interbonded diamond crystals. The catalyst may be provided in the form of a powder intermixed with the diamond crystals or it may be included in an adjacent element from which it infiltrates through the spaces between the diamond crystals during the sintering process. For example, one way the catalyst can be provided is by placing diamond grit on a substrate comprising a cemented tungsten carbide having 5-20 weight percent binder of cobalt or cobalt-nickel and then subjecting these components to high temperatures and pressures so that a portion of the binder of the cemented tungsten carbide infiltrates the diamond grit and catalyzes diamond to diamond bonding. Some of the binder (e.g. cobalt or cobalt-nickel) is left in the PCD.
PCBN, which is sufficiently electrically conductive to be EDM machined, may be used in the present invention as a superhard material for lining in the AWJ mixing tube longitudinal bore. PCBN may be produced in a manner similar to that used for producing PCD.
A particular advantage of PCD over other types of diamond is its ability to be machined by EDM due to its electrically conductive metallic content. The present invention takes advantage of this characteristic and comprises a method of producing an AWJ mixing tube having a longitudinal bore lined with a superhard material, the method comprising the steps of providing at least one superhard material body and then EDM machining the at least one superhard material body to form the longitudinal bore of the AWJ mixing tube. Preferably, the present invention includes providing the longitudinal bore with a tapered entryway by EDM machining so as to facilitate the entry of the high velocity water jet and the abrasive grit into the AWJ mixing tube longitudinal bore. Also according to the present invention, any necessary machining of the external dimensions of the superhard material-cored AWJ mixing tube such as, for example, to permit the mixing tube to fit into an AWJ machining head or to provide desirable external features such as an exit end taper, is done prior to, concurrently with or subsequent to the machining of the mixing tube longitudinal bore.
As used herein, the xe2x80x9cflow passagexe2x80x9d of an AWJ mixing tube is the conduit which extends from one end of the mixing tube to the other through which the high velocity water jet and abrasive grit enter, travel through, and exit the mixing tube. The flow passage includes a longitudinal bore and may also include a tapered entryway. However, when the term xe2x80x9cflow passagexe2x80x9d is used in describing a single component of an AWJ mixing tube, the term refers to the conduit that extends from one end of the component to the other through which the high velocity water jet and abrasive grit enter, travel through, and exit the component. As used herein, the term xe2x80x9ccomponentxe2x80x9d refers to a discrete, hollow segment comprising a portion of the length of an AWJ mixing tube; components are connected together to form a multi-component AWJ mixing tube.
As used herein, the term xe2x80x9cflow-through directionxe2x80x9d is the direction the high velocity water jet and abrasive grit travel through the AWJ mixing tube.
The present invention includes AWJ mixing tubes having a superhard material lining at least part of the AWJ mixing tube""s flow passage. Such AWJ mixing tubes comprise a superhard material lining at least a part of at least one of the tapered entryway and the longitudinal bore of the AWJ mixing tube. In some embodiments, a superhard material lines the entire length of the longitudinal bore and/or the tapered entryway. In other embodiments, a superhard material lines only part of the longitudinal bore length and/or the tapered entryway while the rest of the longitudinal bore length and/or tapered entryway is lined with another type of abrasion-resistant material. The part or parts of the flow passage of the AWJ mixing tube which are to be lined with superhard material rather than some other type of abrasion-resistant material are those part or parts which the user of the AWJ mixing tube desires most to protect from erosion during use.
Although the present invention includes methods for producing AWJ mixing tubes which are comprised solely of a superhard material, it also includes methods for producing AWJ mixing tubes in which the superhard material is surrounded substantially along the length of the mixing tube with a durable material which can act to reduce the susceptibility of the mixing tube to damage from external forces or to facilitate the adaptation of the superhard material into the AWJ machining head. The durable material may also function to reinforce the superhard material so as to prevent the AWJ mixing tube from being damaged by water jet back pressure should the mixing tube become plugged during operation. The present invention also includes methods for producing AWJ mixing tubes which comprise at least one jacket which acts to reduce the susceptibility of the AWJ mixing tube from impact damage or to facilitate the adaptation of the AWJ mixing tube into the AWJ machining head.
Accordingly, the present invention also comprises the steps of surrounding at least one superhard material body substantially along the length of the AWJ mixing tube with a durable material. In one embodiment, in the completed AWJ mixing tube, the durable material will extend beyond the superhard material at the entrance end of the mixing tube with a tapered entryway portion of the mixing tube being formed at least partially in the durable material and the method of the present invention includes forming the mixing tube in this fashion. The durable material is preferably a steel or, more preferably, a cemented tungsten carbide. When the tapered entryway is formed at least partially in the durable material and the durable material is a steel, it is desirable that the steel be an erosion-resistant alloy steel or tool steel.
When cemented tungsten carbide is used as the durable material, in the above one embodiment of the present invention includes the steps of (1) providing at least one composite body comprising a superhard material layer bonded to a cemented tungsten carbide substrate; (2) providing at least one durable material body; (3) bonding the at least one composite body to the at least one durable material body so as to form an AWJ mixing tube blank having a superhard material core; (4) EDM forming a tapered entryway into one end of the AWJ mixing tube blank; and (5) EDM machining a longitudinal bore through the superhard material core of the AWJ mixing tube blank. The method may further comprise the step of machining the external shape of the AWJ mixing tube blank in one or more operations to adapt the AWJ mixing tube blank to fit into an AWJ water jet machining head and to otherwise obtain the final dimensions of the AJW mixing tube. Note that the term xe2x80x9cAWJ mixing tube blankxe2x80x9d is used herein to refer to a single body, whether of a monolithic or a composite construction, from which an AWJ mixing tube may be formed in one or more operations and includes partially formed AWJ mixing tubes up until the last forming operation has been completed.
In this embodiment, the durable material body is provided as a single round rod having a u-shaped channel adapted for receiving the at least one strip of composite material. However, the present invention also includes providing the durable material in other shapes. The present invention also includes providing a plurality of durable material bodies which can surround and be bonded to the one or more superhard material bodies. What is important is that the resulting AJW mixing tube blank have a superhard material core into which a longitudinal bore may be formed such that the longitudinal bore will be lined with superhard material all along the length of the mixing tube, with the possible exception that, in the final AWJ mixing tube, the endmost part of the entryway length in some embodiments may not be lined with a superhard material. In some of those embodiments in which the endmost part of the entryway length is not lined with a superhard material, the present invention also includes coating the exposed durable material in the endmost part of the entryway with a hard coating deposited by vapor deposition, i.e. by physical vapor deposition (PVD) and/or chemical vapor deposition (CVD). Examples of such hard coatings include, without limitation, diamond, titanium nitride, titanium carbide, titanium carbonitride, titanium aluminum nitride, aluminum oxide, and their combinations.
The present invention also comprises AWJ mixing tubes comprising a superhard material including those AWJ mixing tubes in which the superhard material is surrounded substantially along the length of the mixing tube with a durable material which can act to reduce the susceptibility of the mixing tube to damage from external forces, to facilitate the adaptation of the superhard material into the AWJ machining head or to reinforce the superhard material so as to prevent the AWJ mixing tube from being damaged by water jet back pressure should the mixing tube become plugged during operation. The present invention also includes AWJ mixing tubes comprising an entryway piece having a superhard material formed on a tapered entryway bonded to an AWJ mixing tube body piece having a longitudinal bore lined with a superhard material and methods of making such AWJ mixing tubes.
The present invention includes AWJ mixing tubes, and methods for making same, comprising a flow passage formed by EDM in at least one abrasion-resistant material piece, wherein at least part of the flow passage has a lining comprising a superhard material. Included among these AWJ mixing tubes are single-component AWJ mixing tubes as well as multi-component AWJ mixing tubes which comprise a plurality of components and at least one connection, which may be a disconnectable connection, connecting one component to another such that the flow passages of each of the individual components communicate with each other to form the flow passage of the AWJ mixing tube and wherein the flow passage of least one of the plurality of components has a lining comprising a superhard material. As already mentioned, as used herein, the term xe2x80x9ccomponentxe2x80x9d refers to a discrete, hollow segment comprising a portion of the length of an AWJ mixing tube. Each component has a flow passage which is part of the flow passage of the AWJ mixing tube. The components are connected end-to-end with each other to make the AWJ mixing tube. For example, a two-component AWJ mixing tube according to the present invention may have an entryway piece connected to an AWJ mixing tube body piece wherein the entryway piece and the AWJ mixing tube body piece each has a flow passage formed in one or more abrasion-resistant pieces and at least one of the entryway piece and the AWJ mixing tube body piece has part of its flow passage comprising a superhard material. It is to be understood that, as used herein, an AWJ mixing tube is considered to have a plurality of connected components having at least one connection if, and only if, the AWJ mixing tube comprising those components and connection or connections is an integral unit which can be handled and loaded into an AWJ cutting head as a single piece.
The present invention also includes AWJ systems having a mixing tube comprising a superhard material. Such AWJ systems include AWJ systems having an AWJ mixing tube which includes a flow passage formed by EDM in at least one abrasion-resistant material wherein at least part of the flow passage has a lining comprising a superhard material. These AWJ systems include those AWJ systems having AWJ mixing tubes which comprise a plurality of components and at least one connection, which may be a disconnectable connection, connecting one component to another such that the flow passages of each of the individual components communicate with each other to form the flow passage of the AWJ mixing tube and wherein the flow passage of least one of the plurality of components has a lining comprising a superhard material. Such AWJ systems use any type of abrasive particles including, without limitation garnet, olivine, alumina, cubic boron nitride, zirconia, silicon carbide, boron carbide, diamond, other minerals and ceramics, and their mixtures and combinations.
The present invention includes methods of using an AWJ system comprising the steps of providing an AWJ mixing tube having a flow passage formed by EDM in at least one abrasion-resistant material wherein at least part of the flow passage has a lining comprising a superhard material, providing abrasive particles, emitting the abrasive particles from the AWJ mixing tube, and machining a workpiece with the emitted abrasive particles. Such a provided AWJ mixing tube may be one which comprises a plurality of components and at least one connection, which may be a disconnectable connection, connecting one component to another such that the flow passages of each of the individual components communicate with each other to form the flow passage of the AWJ mixing tube and wherein the flow passage of least one of the plurality of components has a lining comprising a superhard material. For example without limitation, the present invention also includes methods of using an AWJ system comprising the steps of providing an abrasive water jet mixing tube having a longitudinal bore lined with a superhard material, providing abrasive particles, emitting the abrasive particles from the abrasive water jet mixing tube, and machining a workpiece with the emitted abrasive particles.
Although AWJ systems typically use water as the carrier fluid, the present invention also contemplates the application of its methods, AWJ mixing tubes, and AWJ systems with the use of any fluid (gaseous or liquid) which is capable of acting as a fluid carrier in a system which uses fluid-carried abrasive particles for cutting or machining a workpiece. Such fluids include those which are capable of replacing water, in whole or in part, as the carrier fluid in an AWJ system. Accordingly, the term xe2x80x9cabrasive water jetxe2x80x9d as used herein is not limited to abrasive jets using water as the carrier fluid but instead refers to any abrasive jet having a fluid carrier.
The present invention also comprises a tubular elongate superhard material body, and methods for making same, wherein the tubular elongate superhard material body has at least one bore formed by EDM which is substantially parallel to the longitudinal axis of the tubular elongate superhard material body.
The present invention also comprises superhard material cylinders having lengths of about 0.2 inches (5 mm) and diameters of about 0.2 inches (5 mm) and either a straight or conical passage or a combination of a straight and conical passage, along their longitudinal centerlines, formed by EDM machining. Such superhard material cylinders comprise a superhard material or a composite of a superhard material bonded to another abrasion-resistant material. Where a superhard material cylinder contains a straight passage, either alone or in conjunction with a conical passage, preferably the aspect ratio of the cylinder length to the diameter of the passage is at least 4 to 1, and more preferably at least 6 to 1, and most preferably at least 10 to 1
These and other features and advantages inherent in the subject matter claimed and disclosed will become apparent to those skilled in the art from the following detailed description of presently preferred embodiments thereof and to the appended drawings.